The present invention relates to an improved process for concentrating elemental lead in crude lead bullion, and, more particularly, to an improved process involving sodium addition to molten bullion at a temperature of at least about 750.degree. C. but not higher than the boiling point of sodium followed by controlled solidification of the resulting mixture to substantially separate a matte equilibrium phase and a copper speiss equilibrium phase from a lead bullion equilibrium phase, the improvement comprising adding previously isolated copper speiss to the molten crude lead bullion prior to or substantially simultaneously with the sodium whereby formation of the equilibrium phases is enhanced. The present invention is particularly applicable for separating elemental lead from relatively pure crude bullions, i.e., bullions which ordinarily contain no more than about 1.3% by weight sulfur as sulfide, or otherwise lack a suitable reagent for the sodium to reduce, by enhancing production of the non-bullion components with their subsequent isolation and recovery.
The introduction of sodium into molten crude bullion and the formation of matte, speiss and bullion equilibrium phase and their subsequent isolation is described in U.S. Pat. No. 4,404,026. The crude bullion described therein is relatively impure, i.e., it contains in excess of about 1.3% by weight sulfur and generally up to as much as 2.6% by weight sulfur as either lead sulfide or copper sulfide. When the sulfur content of the crude bullion is below about 1.3% by weight, however, the introduction of sodium becomes substantially less effective in forming respective isolatable phases, with a bullion phase having an unsatisfactorily high concentration of residual arsenic, and a matte phase having a low copper to lead ratio.